Browsing by Author "Geremew, Akewake"

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    Nutritional evaluation of some Ethiopian oilseed cakes in the diets of juvenile Nile tilapia, Oreochromis niloticus L.
    (Addis Ababa University, 2015-05) Geremew, Akewake; Getahun, Abebe(PhD)
    This study evaluated the suitability of Niger seed cake (NSC) and linseed cake (LSC) inclusion as potential plant protein sources in Nile tilapia, Oreochromis niloticus, diets. A series of four experiments were conducted in a recirculation system using juvenile O. niloticus. The fish were fed diets containing the oilseed cakes at dietary inclusion levels ranging from 20% to 50%. Diets were formulated to be isonitrogenous (32g 100 g-1), isolipidic (10g 100 g-1) and isoenergetic (18 kJ g-1) and fed to juvenile Nile tilapia at 4-10% of their body weight per day for a period of 8 weeks. Niger seed cake (NSC) and linseed cake (LSC) were used individually or as mixtures to test for their effect on Nile tilapia growth and feed utilization. Also of interest was to compare digestibility and feeding values of NSC and LSC with that of soybean cake (SBC), the best plant protein source. Proximate analysis showed that Niger seed cake (NSC) and linseed cake (LSC) had 324.2 and 310.0 g kg-1 crude protein, 201.1 and 136.3 g kg-1 crude fibre and 18.1 and 18.6 kJ g-1 gross energy, respectively. Nutrient digestibility of these oilseed cakes suggested that Nile tilapia may be able to utilize NSC better as dietary protein source due to a reasonably high protein digestibility coefficient (72.6%) than linseed cake (62.4%). Of the three oilseed cakes (NSC, LSC and SBC) tested soybean cake (SBC) produced significantly (P< 0.05) the highest nutrient digestibility coefficients. When Niger seed cake (NSC) and linseed cake (LSC) were used individually as protein sources in Nile tilapia diets, depressed growth and feed efficiency were observed at dietary inclusion levels above 20%. This may be attributed to high levels of antinutritional factors (ANFs), high crude fibre content and poor essential amino acid profile. However, the use of mixtures of these two oilseed cakes (formulation 1 (F1): 50% NSC:50% LSC, Formulation 2 (F2): 33% NSC:67% LSC and Formulation 3 (F3) 67% NSC:33% LSC) was found to be marginally suitable than that of single sources, especially when the proportion of NSC in the mixture is 50% to 67%. The oilseed cake formulations with higher proportion of NSC could be included at 25% dietary inclusion without significantly reducing performance. This may have been as a result of lower levels of ANFs and improvements in the amino acid profile due to mixing. It can be concluded that there is nutritional and economic justification for using NSC and LSC as protein sources in Nile tilapia diets. Based on growth performance, nutrient utilization and economic benefits the diet with F3 formulation at 25% level of inclusion has the best prospects for use in Nile tilapia diets
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    Taxonomic Revision, Relative Abundance, and aspects of the Biology of Some Species of the Genus Garra, Hamilton 1922 (Pisces: Cyprinidae) in Lake Tana, Ethiopia
    (Addis Ababa University, 2007-08) Geremew, Akewake; Getahun, Abebe(PhD); Dejen, Eshete (PhD)
    Taxonomic revision, relative abundance, reproductive biology, length-weight relation, condition factor and aspects of feeding of Lake Tana Garra species were studied from 2187 fish collected during January to December, 2006. Morphological, psychometric and mesmeric characters were used to revise the taxonomy of the three already described species (G. tana, G. dembecha and G. regressus) and one different form of Garra (small mouth, sm). Cluster and principal component analyses using 23 external and 14 skull bone morphometric measurements revealed that G. tana and G. regressus are separate dissimilar species from others. G. dembecha and G. sm showed some similarities, though the few meristic and morphological features were important to differentiate them. The % IRI (Index of Relative Importance) indicated that G. tana is abundant in the pelagic sites whereas G. sm is abundant in the littoral, and sub littoral sites having the rest of Garra species less abundant. Gonad-somatic index (GSI) and % frequency of ripe females were used to determine main breeding season. The main breeding time of G. regresses (April-October), G. tana (March-July) and G. December (May-July) was coincident with the rainy season of the area. G. sm was found to breed intensively during the dry season (November-March). G. tana is capable of breeding throughout the year, whereas G. December breeds only for three months. Extended breeding times were observed in G. sm and G. regresses. Significant differences were observed between the species for both sexes in the mean size at maturity, except for G. sm and G. December. Absolute fecundity was found to be related rectilinear with standard length and linearly with body and gonad weight for G.sm Regress and G. tana. The range of absolute fecundity was (538.9-2968), (606-3397), (1215-1229) and (580.8-1800) for G. tana, G. sm, G. dembecha and G. regressus, respectively. The average relative fecundity was 63.3, 77.1, 102.7, and 55.5 for G. dembecha, G. sm, G. tana and G. regressus, respectively. Both relative and absolute fecundity were statistically different (P< 0.001) between the species. Egg size frequency distribution revealed that G. regresses was found to be multiple spawner, while G. December; G. tana and G. sm were single spanners. Except for G. December and G. regresses (Chi-square, P< 0.05), the sex ratio in the total catch was not different from 1:1 for the other two species. The relationship between standard length and total weight was curvilinear for all the species, and isometric growth was assumed for all. A significant seasonal fluctuation (P< 0.0001) was observed in the condition of all Garra species. The better condition of these fishes during late dry and pre-rainy seasons was attributed to the increase in temperature and availability of food. Microscopic examination of gut contents of G. sm, G. tana and G. December indicated that green, blue-green, diatoms and zooplanktons that are detrimental in their origin were dominant. Key words and phrases: Condition factor, Food items, Garra, Lake Tana, Length-weight relation,Relative abundance, Reproductive biology, and Taxonomic revision.